MILWAUKEE -- Republican Donald Trump emerged from Wisconsin as a damaged front-runner following a crushing primary loss to rival Ted Cruz, deepening questions about the billionaire businessman's presidential qualifications and pushing the Republican Party toward a rare contested convention nomination fight.
Democrat Bernie Sanders also scored a sweeping victory Tuesday in Wisconsin's primary that gives him a fresh incentive to keep challenging Hillary Clinton. But Sanders still lags significantly behind Clinton in the all-important delegate count.
Both parties were turning their sights toward New York, which offers a massive delegate prize in its April 19 contests. It marks a homecoming of sorts for several candidates, with Trump, Clinton and Sanders all touting roots in the state.
Trump, who has dominated the Republican race for months, suddenly finds himself on the defensive as the race moves east. He's struggled through a series of missteps, including his campaign manager's legal issues after an altercation with a female reporter and his own awkward explanation of his position on abortion.
Exit polls in Wisconsin highlighted the deep worries about Trump surging through some corners of the Republican Party. A majority of Republican voters said they're either concerned about or scared of a potential Trump presidency, according to surveys conducted by Edison Research for The Associated Press and television networks.
Cruz has stepped forward as the candidate best positioned to block Trump, though it would likely take a convention battle to accomplish that goal. An ultraconservative Texas senator with a complicated relationship with Republican leaders, Cruz cast his Wisconsin victory as a "turning point" in the race and urged the party to rally around his candidacy.
"We've got the full spectrum of the Republican Party coming together and uniting behind this campaign," he said.
Trump was unbowed in his defeat. His campaign put out a biting statement accusing Cruz of being "worse than a puppet -- he is a Trojan horse, being used by the party bosses attempting to steal the nomination from Mr. Trump."
Sanders still trails Clinton in the pledged delegate count and has so far been unable to persuade superdelegates-- the party officials who can back any candidate -- to drop their allegiance to the former secretary of state and back his campaign.
At a raucous rally in Wyoming, Sanders cast his victory as a sign of mounting momentum for his campaign.
"With our victory tonight in Wisconsin, we have now won 7 out of 8 of the last caucuses and primaries," he declared. Sanders is favoured to win Wyoming's Democratic caucuses on Saturday, but it offers a small delegate prize.
With an overwhelming white electorate and liberal pockets of voters, Wisconsin was favourable territory for Sanders. In a sign of Clinton's low expectations in the Midwestern state, she spent Tuesday night at a fundraiser with top donors in New York City.
Clinton congratulated Sanders on Twitter and thanked her supporters in Wisconsin. "To all the voters and volunteers who poured your hearts into this campaign: Forward!" she wrote.
Because Democrats award delegates proportionally, Sanders' victory in Wisconsin did not cut significantly into Clinton's lead in the pledged delegate count. With 86 delegates at stake in Wisconsin, Sanders will pick up at least 45 and Clinton will gain at least 31.
That means Sanders must still win an unlikely 67 per cent of the remaining delegates and uncommitted superdelegates in order to win the Democratic presidential nomination. The state-by-state nominating contests are choosing delegates who will select the presidential nominees at the parties' national conventions in July.
With most of Wisconsin's delegates allotted, Clinton now has 1,274 delegates to Sanders' 1,025, based on primary and caucus results alone. When including superdelegates, Clinton has a wider lead -- 1,743 to 1,056. It takes 2,383 delegates to win the nomination.
Clinton's campaign has cast her overall lead as nearly insurmountable. Yet Sanders' continued presence in the race has become an irritant for Clinton, keeping her from turning her attention to the general election.
In the Republican race, Cruz won at least 33 Wisconsin delegates, while Trump carried at least three. Six delegates are still up for grabs, pending the outcome in two congressional districts.
With Wisconsin results included, Trump led with 740 delegates to Cruz's 514, while Ohio Gov. John Kasich had 143. It takes 1,237 delegates to win the nomination.
Trump still has a narrow path to claim the nomination by the end of the primaries on June 7. But by losing Wisconsin, the real estate mogul has little room for error in upcoming contests. He must win 57 per cent of the remaining delegates to win the nomination before the convention. So far, he is winning just 46 per cent.
Complicating the primary landscape for both Cruz and Trump is Kasich's continuing candidacy. The Ohio governor's only victory has come in his home state, but he's still picking up delegates that would otherwise help Trump inch closer to the nomination or help Cruz catch up.
Despite the concern among some Wisconsin Republicans about Trump becoming president, nearly 6 in 10 Republican voters there said the party should nominate the candidate with the most support in the primaries, which so far would be Trump.